U.S. patent application number 10/584754 was filed with the patent office on 2007-07-19 for ballistic-resistant article.
Invention is credited to Martinus Johannes Nicolaas Jacobs, Reinard Jozef Maria Steeman.
Application Number | 20070163023 10/584754 |
Document ID | / |
Family ID | 34748223 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070163023 |
Kind Code |
A1 |
Steeman; Reinard Jozef Maria ;
et al. |
July 19, 2007 |
Ballistic-resistant article
Abstract
The invention relates to a preformed sheet comprising at least
two mono-layers, each mono-layer containing unidirectionally
oriented fibers having a tensile strength of at least about 1.2 GPa
and a tensile modulus of at least 40 GPa, and a binder, with a
fibre direction in each mono-layer being rotated with respect to
the fibre direction in an adjacent mono-layer, and a separating
film on both outer surfaces, characterized in that the separating
film has a porosity of between 40 and 90%. With this preformed
sheet assemblies and articles offering a substantially higher
ballistic protection level at a certain weight can be obtained. The
invention further relates to an assembly of at least two such
sheets and to a flexible ballistic-resistant article comprising
said assembly.
Inventors: |
Steeman; Reinard Jozef Maria;
(Elsloo, NL) ; Jacobs; Martinus Johannes Nicolaas;
(Heerlen, NL) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Family ID: |
34748223 |
Appl. No.: |
10/584754 |
Filed: |
January 1, 2004 |
PCT Filed: |
January 1, 2004 |
PCT NO: |
PCT/NL04/00028 |
371 Date: |
September 8, 2006 |
Current U.S.
Class: |
2/2.5 |
Current CPC
Class: |
B32B 2307/54 20130101;
B32B 5/26 20130101; B32B 2307/514 20130101; B32B 7/02 20130101;
B32B 5/02 20130101; B32B 27/02 20130101; B32B 27/12 20130101; F41H
5/0478 20130101; B32B 2262/0253 20130101; B32B 2307/518 20130101;
B32B 2571/02 20130101 |
Class at
Publication: |
002/002.5 |
International
Class: |
F41H 1/02 20060101
F41H001/02 |
Claims
1. Preformed sheet comprising at least two mono-layers, each
mono-layer containing unidirectionally oriented fibers having a
tensile strength of at least about 1.2 GPa and a tensile modulus of
at least 40 GPa, and a binder, with a fibre direction in each
mono-layer being rotated with respect to the fibre direction in an
adjacent mono-layer, and a separating film on both outer surfaces,
characterized in that the separating film has a porosity of between
40 and 90%.
2. Preformed sheet according to claim 1, wherein the fibres
comprise high-performance polyethylene fibres.
3. Preformed sheet according to claim 1, wherein the binder
consists essentially of a thermoplastic elastomer and has a tensile
modulus of less than about 40 MPa.
4. Preformed sheet according to claim 1, wherein the separating
film is made from ultra-high molar mass polyethylene.
5. Preformed sheet according to claim 1, wherein the separating
film is a biaxially stretched film.
6. Preformed sheet according to claim 1, wherein the separating
film has an areal density of between 2 and 4 G/M.sup.2.
7. A preformed sheet according to claim 1, wherein the separating
film has a strength factor of at least 150 N/m.
8. A preformed sheet according to claim 1, comprising two
mono-layers of unidirectionally oriented fibres.
9. Assembly of at least two sheets according to claim 1, which are
not linked to one another.
10. Flexible ballistic-resistant article comprising at least one
assembly of claim 9.
11. Flexible ballistic-resistant article comprising an assembly,
which contains a plurality of sheets containing at least two
mono-layers, each mono-layer consisting essentially of
unidirectionally oriented high-performance polyethylene fibres
having a tensile strength of at least 1.2 GPa, with the fibre
direction in each mono-layer being rotated with respect to the
fibre direction in an adjacent mono-layer, and two polyethylene
separating films having a porosity of between 40 and 90% on both
outer surfaces, the assembly having an areal density of at least
1.5 kg/m.sup.2 and a specific energy absorption of at least 300
J.m.sup.2/kg as measured against a 9.times.19 mm FMJ Parabellum
bullet according to a test procedure based on Stanag 2920.
Description
[0001] The invention relates to a preformed sheet, to an assembly
of at least two sheets and to a flexible ballistic-resistant
article comprising said assembly. A preformed sheet comprises at
least two mono-layers, each mono-layer containing unidirectionally
oriented fibres having a tensile strength of at least about 1.2 GPa
and a tensile modulus of at least 40 GPa, and a binder, with a
fibre direction in each mono-layer being rotated with respect to
the fibre direction in an adjacent mono-layer, and a separating
film on both outer surfaces.
[0002] Such a preformed sheet is known from EP 0907504 A1. EP
0907504 A1 describes a composite layer (or preformed sheet), which
was produced by cross-wise stacking of 4 monolayers and applying a
separating film made from a linear low-density polyethylene, and
subsequently consolidating the stack at elevated temperature under
pressure. The mono-layers containing unidirectionally oriented
fibres were produced by aramid yarn fibres having a titer of 1680
dtex being guided from a bobbin frame over a comb and wetting them
with an aqueous dispersion of a
polystyrene-polyisoprene-polystyrene block copolymer as a binder or
matrix material. Flexible ballistic-resistant shaped articles were
made from a non-linked stack of several of said composite layers,
the stack being stabilized by stitching at the corners.
[0003] A drawback of the preformed sheet known from the prior art
is that the ratio between energy absorption of a
ballistic-resistant article comprising said sheets, which is a
measure for the ballistic protection level, and the weight of the
ballistic resistant article is unfavourable. This ratio is
generally expressed as the specific energy absorption (SEA), that
is the energy absorbed per areal mass (generally called areal
density (AD)). This implies that a relatively heavy
ballistic-resistant article is required to achieve a certain
desired protection level. If the ballistic-resistant article, on
the other hand, has a low weight, the article provides a relatively
low protection level against ballistic hits. For a large number of
applications the lowest possible weight of the ballistic
resistant-article in conjunction with a certain minimum protection
level is of great importance. This is the case, for example, in the
field of personal protection, such as clothing and body armour,
like for example bullet-proof vests; but also for application in,
for example, vehicles.
[0004] There is thus a constant need in industry for a preformed
sheet that enables making of ballistic-resistant articles offering
a higher protection level at a certain weight of the article.
[0005] According to the present invention, this is provided by a
preformed sheet wherein the separating film has a porosity of
between 40 and 90%.
[0006] With the preformed sheet according to the invention, a
substantially higher protection level at a certain weight of an
assembly of sheets or a ballistic-resistant article comprising an
assembly of sheets according to the invention can be obtained. A
further advantage of the preformed sheet according to the invention
is that, in addition to having a favourable ratio between the
protection level and the areal density, a ballistic-resistant
article comprising an assembly of the preformed sheets offers more
flexibility, which increases the scope for applications of such
ballistic-resistant articles. This makes the article particularly
suitable for applications where high flexibility and comfort-in-use
is desirable, such as in body armour. The sheets further show
improved printability with different techniques, which is an
advantage in view of production and quality control and tracability
issues.
[0007] With ballistic-resistant articles are meant shaped parts,
comprising an assembly of at least two preformed sheets according
to the invention, which can be used as, for example, protective
clothing or for armouring of vehicles, and which offer protection
against ballistic impacts such as by bullets and shrapnels.
[0008] An assembly according to the invention contains a stack of
preformed sheets that are not linked to one another; that is, the
sheets are not attached or adhered to each other over a substantial
part of their adjacent surfaces. It is, however, difficult to
handle a stack of preformed sheets that are not linked to one
another, because such stack lacks any coherence required for
further processing. To achieve some level coherence the
ballistic-resistant article can, for example, be stitched through.
Such stitching is done as little as possible, however, for example
only at the corners or around the edges, in order to allow some
movement of sheets relative to each other. Another possibility is
to enclose the stack of preformed sheets in a flexible cover or
envelop. Thus the preformed sheets in the assembly or in the
ballistic resistant article remain able to shift with respect to
one another, whereas the assembly or article in itself does have
coherence and shows good flexibility.
[0009] A preformed sheet comprises at least two mono-layers of
unidirectionally oriented fibres, with a fibre direction in each
mono-layer being rotated with respect to the fibre direction in an
adjacent mono-layer, and the at least two mono-layers being linked
or attached to one another. The angle of rotation, which means the
smallest angle enclosed by the fibres of the adjacent mono-layers,
is between 0.degree. and 90.degree.. Preferably, the angle is
between 45.degree. and 90.degree.. Most preferably, the angle is
between 80.degree. and 90.degree.. Ballistic-resistant articles in
which the fibres in the adjacent mono-layers are at such an angle
to one another have better antiballistic characteristics. The term
mono-layer refers to a layer of unidirectionally oriented fibres
and a binder that basically holds the fibres together.
[0010] The term fibre comprises not only a monofilament but, inter
alia, also a multifilament yarn or flat tapes. The term
unidirectionally oriented fibres refers to fibres that, in one
plane, are essentially oriented in parallel.
[0011] The fibres in the preformed sheet of the invention have a
tensile strength of at least about 1.2 GPa and a tensile modulus of
at least 40 GPa. The fibres may be inorganic or organic fibres.
Suitable inorganic fibres are, for example, glass fibres, carbon
fibres and ceramic fibres. Suitable organic fibres with such a high
tensile strength are, for example, aramid fibres, liquid
crystalline polymer fibres and fibres of, for example, polyolefins,
polyvinyl alcohol, and polyacrylonitrile which are highly oriented,
such as obtained, for example, by a gel spinning process. The
fibres preferably have a tensile strength of at least about 2 GPa,
at least 2.5 or even at least 3 GPa. Highly oriented polyolefin
fibres are preferably used. The advantage of these fibres is that
they have both a high tensile strength and a low specific weight,
so that they are in particular very suitable for use in light
weight ballistic-resistant articles.
[0012] Suitable polyolefins are in particular homopolymers and
copolymers of ethylene and propylene, which may also contain small
quantities of one or more other polymers, in particular other
alkene-1-polymers.
[0013] Good results are obtained if linear polyethylene (PE) is
selected as the polyolefin. Linear polyethylene is herein
understood to mean polyethylene with less than 1 side chain per 100
C atoms, and preferably with fewer than 1 side chain per 300 C
atoms; a side chain or branch generally containing at least 10 C
atoms. The linear polyethylene may further contain up to 5 mol % of
one or more other alkenes that are copolymerisable therewith, such
as propene, butene, pentene, 4-methylpentene, octene.
[0014] Preferably, the linear polyethylene is of high molar mass;
with an intrinsic viscosity (IV, as determined on solutions in
decalin at 135.degree. C.) is at least 4 dl/g; more preferably at
least 8 dl/g. Such polyethylene is also referred to as ultra-high
molar mass polyethylene (UHPE). Intrinsic viscosity is a measure
for molar mass (also called molecular weight) that can more easily
be determined than actual molar mass parameters like M.sub.n and
M.sub.w. There are several empirical relations between IV and
M.sub.w, but such relation is highly dependent on molar mass
distribution. Based on the equation M.sub.w=5.37.times.10.sup.4
[IV].sup.1.37 (see EP 0504954 A1) an IV of 4 or 8 dl/g would be
equivalent to M.sub.w of about 360 or 930 kg/mol, respectively.
[0015] High performance polyethylene (HPPE) fibres consisting of
polyethylene filaments that have been prepared by a gel spinning
process, such as described, for example, in GB 2042414 A or WO
01/73173, are preferably used. A gel spinning process essentially
consists of preparing a solution of a linear polyethylene with a
high intrinsic viscosity, spinning the solution into filaments at a
temperature above the dissolving temperature, cooling down the
filaments to below the gelling temperature, such that gelling
occurs, and stretching the filaments before, during or after the
removal of the solvent.
[0016] The term binder refers to a material that binds or holds the
fibres together and may enclose the fibres in their entirety or in
part, such that the structure of the mono-layer is retained during
handling and making of preformed sheets. The binder material can
have been applied in various forms and ways; for example as a film,
as a transverse bonding strip or as transverse fibres (transverse
with respect to the unidirectional fibres), or by impregnating
and/or embedding the fibres with a matrix material, e.g. with a
polymer melt or a solution or dispersion of a polymeric material in
a liquid. Preferably, matrix material is homogeneously distributed
over the entire surface of the mono-layer, whereas a bonding strip
or bonding fibres can be applied locally. Suitable binders are
described in a.o. EP 0191306 B1, EP 1170925 A1, EP 0683374 B1 and
EP 1144740 A1.
[0017] In a preferred embodiment, the binder is a polymeric matrix
material, and may be a thermosetting material or a thermoplastic
material, or mixtures of the two. The elongation at break of the
matrix material is preferably greater than the elongation of the
fibres. The binder preferably has an elongation of 3 to 500%.
Suitable thermosetting and thermoplastic matrix materials are
enumerated in, for example, WO 91/12136 A1 (pages 15-21). From the
group of thermosetting polymers, vinyl esters, unsaturated
polyesters, epoxides or phenol resins are preferably selected as
matrix material. From the group of thermoplastic polymers,
polyurethanes, polyvinyls, polyacrylics, polyolefins or
thermoplastic elastomeric block copolymers such as
polyisopropene-polyethylene-butylene-polystyrene or
polystyrene-polyisoprene-polystyrene block copolymers can be
selected as matrix material. Preferably the binder consists
essentially of a thermoplastic elastomer, which preferably
substantially coats the individual filaments of said fibres in a
monolayer, and has a tensile modulus (determined in accordance with
ASTM D638, at 25.degree. C.) of less than about 40 MPa. Such a
binder results in high flexibility of a mono-layer, and of an
assembly of preformed sheets. It was found that very good results
are obtained if the binder in the mono-layers and preformed sheet
is a styrene-isoprene-styrene block copolymer.
[0018] In a special embodiment of the invention, the binder in the
preformed sheet according to the invention also contains, in
addition to the polymeric matrix material, a filler in an amount of
from 5 to 80% by volume, calculated on the basis of the total
volume of the binder. More preferably, the amount of filler is from
10 to 80% by volume and most preferably from 20 to 80% by volume.
It was found that as a result, the flexibility of the ballistic
resistant article increases without significant adverse effects on
the antiballistic characteristics.
[0019] The fillers do not contribute to the bonding between the
fibres, but rather serve for volumetric dilution of the matrix
between the fibres, as a result of which the ballistic resistant
article is more flexible and has higher energy absorption. The
filler preferably comprises a finely dispersed substance having a
low weight or density. The filler may be a gas, although using a
gas as filler presents practical problems in processing the matrix
material. The filler may also, inter alia, comprise the substances
customary for preparing dispersions, such as emulsifiers,
stabilizers, binders and the like or a finely dispersed powder.
[0020] It was found that if the binder contains an amount of filler
below 80% by volume, the amount of binder is sufficient to achieve
adequate bonding between the fibres, with a constant total quantity
of matrix material. It was also found that if the matrix contains a
quantity of filler greater than 5% by volume, the flexibility of
the ballistic resistant article increases.
[0021] Preferably, the amount of binder in the mono-layer is at
most 30 mass %, more preferably at most 25, 20, or even at most 15
mass %; since the fibres contribute most to ballistic
performance.
[0022] The preformed sheet of the invention comprises separating
films with a porosity of between 40 and 90% on both outer surfaces.
Said films can be for example porous polyethylene, polypropylene or
polytetrafluoroethylene films, the preparation of which is
described in e.g. EP 0184392 A1 and EP 0504954 A1. Porosity of a
film is the relative volume of the voids, pores or channels in the
film (expressed in volume percentage), as determined from density
measurements. Porosity of a film can be determined most
conveniently before it is applied in the preformed sheet; porosity
may also be reduced during laminating under pressure to form the
preformed sheet. During lamination or pressure such conditions
(temperature, pressure, time) are chosen, that a consolidated sheet
is obtained; that is all layers at least partly adhering to each
other, but without substantially melting the separating film as
this would deteriorate porosity and mechanical properties of the
film.
[0023] Preferably, the separating film has an initial porosity,
that is before making the preformed sheet, of at least 50%, 60 or
even at least 70%.
[0024] Preferably, the films are so-called micro-porous films,
meaning that the pores and channels in the essentially continuous
matrix structure have a size between about 0.001 and 10 micron,
preferably between about 0.01 and 5 micron.
[0025] The separating film is a preferably made from a polyolefin,
more preferably a polyethylene. There are many different
polyethylene grades that are very suited for forming into thin
films; including different types of copolymers of ethylene and at
least one comonomer, like an alpha-olefin. In a preferred
embodiment, the separating film is essentially made from a high
molar mass polyethylene, more preferably form an ultra-high molar
mass polyethylene (UHPE) of IV at least 4 dl/g. Such films show
generally relatively high strength and modulus, and high abrasion
resistance.
[0026] The preformed sheet can further comprise an adhesive layer
between the porous film and other layers, in order to improve
inter-layer adhesion, and thus consistency and stability of the
sheet.
[0027] In a special embodiment of the invention, the preformed
sheet contains mono-layers comprising HPPE fibres and a
polyethylene porous film, more preferably a micro-porous UHPE film.
The advantage of such construction is that good adhesion between
the layers occurs without additional adhesives, thus contributing
to weight reduction. The flexibility of an assembly comprising a
stack of such sheets is furthermore very high, probably because of
very low friction between the surfaces of the sheets. This greatly
improves comfort to the wearer of protective articles made
therefrom.
[0028] Preferably the separating film is a biaxially-stretched
film, more preferably a 10 to 100.times. biaxially-stretched film.
A 10 to 100.times. biaxially-stretched film is herein understood to
be a film, which is stretched in two perpendicular directions such
that the surface of the film increased by a factor 10 to 100. A
method for the manufacturing of said stretched films is described
in EP 0504954 A1. An advantage of biaxially-stretched films is that
an even higher protection level at a certain weight can be
obtained. Preferably, the film is at least 20.times. biaxially
stretched, at least 30.times., or even at least 40.times.. More
preferably, biaxially-stretched films made from UHPE are applied in
the sheets. Such films have relatively high tensile strength and
modulus, which may contribute to deformation of the preformed sheet
upon impact. Tensile properties are preferably expressed per width
of film (e.g. in N/m) and not per cross-section (like N/m.sup.2),
to allow better comparison with non-porous films. Preferably,
therefore, the separating film has a tensile strength per width of
film (herein also called strength factor) of at least 150 N/m, at
least 200, or even at least 250 N/m. In case of films with high
elongation at break (for example greater than 20%) the yield
strength is preferably taken as reference rather than strength at
break. Tensile modulus per width of film is preferably at least
3000 N/m, at least 4000, or even at least 5000 N/m.
[0029] Although the thickness, or mass per surface area (called
areal mass or areal density) of the film is not critical for
ballistic performance, thin films are preferred, since this further
contributes to making lightweight and flexible sheets, assemblies,
and articles. The best results were obtained with a preformed sheet
wherein the separating film has an areal density of between 2 and
8, preferably between 2 and 4 g/m.sup.2.
[0030] The preformed sheet according to the invention comprises at
least two mono-layers containing unidirectionally oriented fibres.
In general, the preformed sheet comprises 2, 4 or another multiple
of 2 perpendicularly oriented mono-layers. Preferably, the
preformed sheet comprises two mono-layers of unidirectionally
oriented fibers combined with a biaxially-stretched film. A
preformed sheet with two mono-layers of unidirectionally oriented
fibers combined with biaxially-stretched films on both outer
surfaces turned out to give the best ballistic protection.
[0031] In a special embodiment of the invention, the preformed
sheet contains as separating films uniaxially stretched films,
preferably films with a stretch ratio of between 10 and 50 . These
uniaxially stretched films are placed such that the stretch
direction of the film is perpendicular to the fibre direction in
the adjacent layer of unidirectional fibres. In such case, the
sheet may contain an uneven number of mono-layers. In a special
embodiment, 3 mono-layers of unidirectional oriented fibres, a
center layer of which can have up to about the same areal density
as both adjacent mono-layers together, have been covered with
uniaxially stretched films, with stretch direction perpendicular to
the fibre direction in the adjacent layer of unidirectional fibres.
The advantage of such construction is, that in a continuous process
of making a sheet via e.g. calandering uniaxially stretched films
onto a stack of monolayers, both separating films can be applied in
the same direction from rolls of sheet.
[0032] The invention further relates to an assembly of at least two
preformed sheets according to the invention, which sheets are not
linked to one another. With increasing number of preformed sheets,
the ballistic protection level is improved, but the weight of the
assembly increases, and the flexibility decreases. In order to
obtain a maximum flexibility, adjacent sheets in an assembly are
not linked to one another. Depending on the threat, and the level
of protection desired the skilled person can find an optimum in the
number of sheets by some experimentation.
[0033] Further advantages of the ballistic-resistant assembly
according to the invention, or article comprising such assembly,
are found in applications in which, in addition to the weight and
the protection level of the ballistic-resistant article, the
flexibility plays an important part.
[0034] Ballistic-resistant assemblies and articles can be employed
both in permanently and in once-only flexible applications.
Permanently flexible applications refer to applications in which
the ballistic-resistant articles as a result of the use
continuously undergo adjustments in shape, such as, for example,
ballistic-resistant articles for use as body armour. Once-only
flexible applications refer to applications in which the
ballistic-resistant assemblies or articles are brought into a
specific shape only once. An example of this is a
ballistic-resistant article that is to be fitted in not readily
accessible spaces such as the inside of car doors.
[0035] It was found that a suitable flexibility, protection level
and weight of the ballistic-resistant assembly is achieved if the
weight of the preformed sheets has a particular maximum value.
Preferably, the weight, or areal density of the preformed sheet in
the ballistic-resistant articles in a permanently flexible
application is at most 500 g/m.sup.2, the fibre content of each
mono-layer being between 10 and 150 g/m.sup.2. More preferably, the
weight of the preformed sheet is at most 300 g/m.sup.2, the fibre
content of each mono-layer being between 10 and 100 g/m.sup.2.
[0036] Once-only flexible applications can make use of a
ballistic-resistant assembly or article that contain preformed
sheets having a weight or areal density of at most 800 g/m.sup.2
and preferably greater than 300 g/m.sup.2, because in this
once-only flexible application a certain minimum stiffness is
desired, so that the applied shape is retained. More preferably,
the weight of the preformed sheets is greater than 400 g/m.sup.2
and still more preferably greater than 500 g/m.sup.2.
[0037] The ballistic-resistant assembly can, in principle, be
fabricated by any known suitable method, for example in accordance
with processes described in WO 95/00318, U.S. Pat. No. 4,623,574,
or U.S. Pat. No. 5,175,040. A mono-layer is produced, for example,
by fibres, preferably in the form of continuous multifilament
yarns, being guided from a bobbin frame across a comb, as a result
of which they are oriented in parallel in a plane. A temporary
support layer, e.g. a coated paper sheet that is removed again from
the mono-layer in a later stage of the process, may be used for
easier processing. A binder is applied to basically hold the fibres
together, that is to retain the fibre orientation and structure as
obtained during further processing steps. If a matrix material is
to be applied as binder, the fibres are preferably coated, before
or after being oriented in parallel in a plane, with an amount of a
liquid substance containing the binder or a precursor therefore,
which in a later stage in the fabrication of the
ballistic-resistant article reacts to give the polymer matrix
material having the desired modulus of elasticity. The term
precursor refers to a monomer, an oligomer or a cross-linkable
polymer composition. The liquid substance may be a solution, a
dispersion or a melt.
[0038] A number of mono-layers is laid with an angle of rotation,
preferably at an angle of about 90.degree., on top of one another,
and a separating film is placed on both surfaces (on top of and
below the stacked mono-layers), a multi-layer sheet being formed in
the process. Preferably, the temperature and/or the pressure is
increased to consolidate the layers using known techniques; this
can for example be done discontinuously by compressing a stack in a
mould, or continuously via laminating and calandering steps. If a
matrix material is applied as binder, the matrix material may thus
be made to flow between the fibres and to adhere to the fibres of
the under- and/or overlying mono-layers, and optionally to the
separating film. If a solution or a dispersion of the matrix
material is employed, the process of forming the mono-layers into a
multi-layer sheet also comprises a step of evaporating the solvent
or dispersant, generally before the steps of placing separating
film layers and consolidation. Then the preformed sheets are
stacked to produce an assembly, which in turn can be applied to
make a ballistic-resistant article, with the option of stabilizing
the assembly by for example local stitching or enveloping the stack
with a flexible cover.
[0039] It was found that, with a view to obtaining a low binder
content, especially a low matrix material content, it is
advantageous to use a method in which the mono-layer is produced by
wetting yarns having a count of yarn (or titer) of between 500 and
2500 dtex with a dispersion of the matrix material and optionally
filler. Yarns having a count of yarn greater than 500 dtex absorb
comparatively little matrix material from the dispersion.
Preferably, the count is greater than 800 dtex, more preferably
greater than 1000 dtex and most preferably greater than 1200 dtex.
The count of yarn is preferably lower than 2500 dtex, because these
yarns can be spread more readily in the plane of the
mono-layer.
[0040] Preferably, an aqueous dispersion of a matrix material is
used. An aqueous dispersion has a low viscosity, which has the
advantage that the matrix material is very uniformly distributed
over the fibres, and good, homogeneous fibre-fibre bonding being
achieved as a result. A further advantage is that the dispersant
water is non-toxic and can therefore be evaporated in the open air.
Preferably, the dispersion, likewise with a view to obtaining a
uniform distribution at the low matrix percentage aimed for,
contains between 30 and 60 mass % of solid components (elastomeric
matrix material and any filler present), relative to the total mass
of the dispersion.
[0041] The ballistic-resistant assembly according to the invention,
obtainable according to the methods described above, shows very
good ballistic properties as expressed by V.sub.50 and SEA values,
especially at relatively low areal density. Preferably, the
assembly according to the invention, or a flexible
ballistic-resistant article comprising such assembly, has a
specific energy absorption (SEA) of at least 300 Jm.sup.2/kg, when
struck by a bullet of type FMJ Parabellum 9.times.19 mm (8 grams).
The energy absorption (EA) upon impact of a bullet or a shrapnel is
calculated from the kinetic energy of a bullet or shrapnel of
velocity V.sub.50. The V.sub.50 is the velocity at which the
probability of the bullets or shrapnels penetrating through the
ballistic structure is 50%.
[0042] The invention more specifically relates to a flexible
ballistic-resistant article comprising an assembly of a plurality
of sheets containing at least two mono-layers consisting
essentially of HPPE multifilament yarn having a tensile strength of
at least about 1.2 GPa and porous polyethylene separating films,
the assembly having an areal density (AD) of at least 1.5
kg/m.sup.2 and a specific energy absorption (SEA) of at least 280
J.m.sup.2/kg as measured against a 9.times.19 mm FMJ Parabellum
bullet according to a test procedure based on Stanag 2920.
Preferably, the article has a SEA of at least 300, 325, 350, or
even at least 375 J.m.sup.2/kg.
[0043] The invention is further explained by means of the following
examples, without being limited thereto, however.
Methods
[0044] IV: the Intrinsic Viscosity is determined according to
method PTC-179 (Hercules Inc. Rev. Apr. 29, 1982) at 135.degree. C.
in decalin, the dissolution time being 16 hours, with DBPC as
anti-oxidant in an amount of 2 g/l solution, by extrapolating the
viscosity as measured at different concentrations to zero
concentration; [0045] Side chains: the number of side chains in a
UHPE sample is determined by FTIR on a 2 mm thick compression
moulded film, by quantifying the absorption at 1375 cm-1 using a
calibration curve based on NMR measurements (as in e.g. EP
0269151); [0046] Tensile properties: tensile strength (or
strength), tensile modulus (or modulus) and elongation at break (or
eab) are defined and determined on multifilament yarns as specified
in ASTM D885M, using a nominal gauge length of the fibre of 500 mm,
a crosshead speed of 50%/min and Instron 2714 clamps, of type Fibre
Grip D5618C. On the basis of the measured stress-strain curve the
modulus is determined as the gradient between 0.3 and 1% strain.
For calculation of the modulus and strength, the tensile forces
measured are divided by the titre, as determined by weighing 10
metres of fibre; values in GPa are calculated assuming a density of
0.97 g/cm.sup.3. Tensile properties of thin films were measured in
accordance with ISO 1184(H). [0047] Porosity of porous films was
calculated from the measured density of the film and the density of
the material from which the film was made (for UHPE a density of
0.97 g/cm.sup.3 was used); [0048] Ballistic performance: V.sub.50
and SEA of composite panels were determined with a test procedure
according to Stanag 2920, using 9 mm*19 mm FMJ Parabellum bullets
(from Dynamit Nobel). An assembly of layers was fixed using
flexible straps on a support filled with Roma Plastilin backing
material, which was preconditioned at 35.degree. C. Trauma effect
was quantified by measuring the depth of back face deformation of
the backing material. Preparation of HPPE Fibres.
[0049] A HPPE multifilament yarn was made by extruding an 8 mass %
solution of a UHPE homopolymer having less than 0.3 side groups per
1000 per carbon atoms and an IV of 19.8 dl/g in decalin containing
a ratio of cis/trans isomers of between 38/62 and 42/58, was made,
and extruded with a 130 mm twin screw extruder equipped with a
gear-pump at a temperature setting of 180.degree. C. through
spinplates having 1176 spinholes with a rate of 2.2 g/min per hole.
The spinholes had an initial cylindrical channel of 3.5 mm diameter
and L/D of 18, followed by a conical contraction with cone angle
60.degree. into a cylindrical channel of 0.8 mm diameter and L/D of
10. The fluid filaments were cooled, after passing an air-gap of 25
mm, in a water bath kept at about 30-40.degree. C. and with a water
flow rate of about 5 cm/s perpendicular to the filaments entering
the bath, and were taken-up at such rate that a draw ratio of 16
was applied to the as-spun filaments in the air-gap. The filaments
were subsequently further drawn in the solid state in two steps;
first in an oven with a temperature gradient of about
110-140.degree. C., and than at about 151.degree. C., applying a
total solid state draw ratio of about 25, during which process the
decalin evaporated from the filaments. The yarns thus obtained had
a titer of 930 dtex, a tensile strength of 4.1 GPa and a modulus of
150 GPa.
COMPARATIVE EXPERIMENT A
[0050] A mono-layer was produced from the HPPE fibres described
above, by guiding several yarns from a bobbin frame over a comb and
wetting the filaments with an aqueous dispersion of Kraton.RTM.
D1107 (polystyrene-polyisoprene-polystyrene block copolymer
thermoplastic elastomer) as matrix material. The yarns were
oriented in parallel in a plane, and after drying the areal density
of the mono-layer was about 38 g/m.sup.2, matrix content was about
12 mass %. A preformed sheet was produced by crosswise stacking 2
monolayers and applying as separating layers on each side a
non-porous linear low-density polyethylene film with a thickness of
7 micron (equivalent to an areal density of about 7 g/m.sup.2), and
consolidating the mono-layers and the separating films at a
pressure of about 0.5 MPa and at a temperature of about
110-115.degree. C. The polyethylene film had a strength at yield of
about 10 MPa, or a strength factor of about 70 N/m.
[0051] A flat ballistic-resistant article was made from a loose,
non-linked assembly of a number of preformed sheets, the assembly
being stitched through at the corners. Ballistic performance for
three different assemblies was tested with a bullet type 9.times.19
mm FMJ Parabellum (8 g); V.sub.50, SEA and trauma (back face
deformation) results are given in Table 1.
EXAMPLE 1
[0052] Comparative experiment A was repeated, but now a 20 micron
thick micro-porous UHPE film, Solupor.RTM. 3P07A having a porosity
83% (obtained from DSM Solutech, NL), was applied as separating
film. This biaxially stretched film had a tensile strength of about
12 MPa, elongation at break of 13% (both in machine direction), and
strength factor of about 240 N/m. The assembled sheets easily
slided over each other, emphasizing the need for some stabilisation
during further processing and testing. The flexibility of the
stabilized assembly was judged as higher; the stack could more
easily be bended than the stack of Comp. Exp. A. Surprisingly,
observed V.sub.50 values, and thus SEA, were markedly higher than
for Comp. Exp. A; whereas trauma not increased.
COMPARATIVE EXPERIMENT B AND EXAMPLE 2
[0053] Comparative experiment A and example 1 were repeated, but
the monolayers had AD of about 39 g/m.sup.2 and matrix content was
about 15 mass %. Test results confirm the improved ballistic
performance of sheets made with porous separating layers, see Table
1.
COMPARATIVE EXPERIMENT C AND EXAMPLE 3
[0054] A unidirectional (UD) mono-layer was made as in Comp. Exp A
with AD of about 20 g/m.sup.2 and matrix content of about 15 mass
%. A preformed sheet was made by placing 4 mono-layers cross-wise
with a polyethylene film of 7 g/m.sup.2 on both sides, and
consolidating by compression at 110-115.degree. C. A number of
these sheets were stacked, stabilized with stitches, and tested on
anti-ballistic performance as before.
[0055] In Example 3 the preformed sheet contained two micro-porous
UHPE films of 8 micron (areal density 3 g/m.sup.2) and porosity 63%
This developmental film was obtained from DSM Solutech, NL, and was
similarly to the Solupor) 3P07A film made with a process as
described in EP 0504954 A1). The assemblies made herefrom show
significantly better ballistic performance than the samples with
non-porous films, see Table 1.
[0056] The improved performance is further exemplified by FIG. 1,
wherein observed SEA values are plotted versus areal density of the
tested assemblies of experiments A, B, 1 and 2. TABLE-US-00001
TABLE 1 Preformed sheet Assembly of sheets Number of Ballistic
results Experi- mono- Number of AD V.sub.50 SEA trauma ment layers
sheets (kg/m.sup.2) (m/s) (J m.sup.2/kg) (mm) Comp. 2 22 2 322 211
37 Exp. A 31 2.6 435 272 48 38 3.4 466 245 34 Example 1 2 24 2 417
350 44 34 2.8 464 305 40 41 3.4 506 300 35 Comp. 2 21 2 333 201 37
Exp. B 29 2.6 426 263 39 36 3.4 458 245 34 Example 2 2 23 2 409 341
40 33 2.8 484 333 38 40 3.4 495 287 33 Comp. 4 21 2 425 365 35 Exp.
C 30 2.8 466 307 35 36 3.4 489 280 35 Example 3 4 23 2 462 429 36
32 2.8 494 352 30 39 3.4 528 329 32
* * * * *